Encoder made of rubber material and method of manufacturing thereof

ABSTRACT

An encoder made of rubber material in which the S-poles and the N-poles are alternately magnetized in circumference, whose magnetic force is strong and whose variation of the magnetic force is slight in the circumferential direction when it is magnetized. And a manufacturing method thereof.  
     A ring shaped rubber compound made of unvulcanized rubber material into which magnetic powders are mixed and having thickness t1 of 1.5 times to 5 times thicker than the thickness t of the encoder made of rubber material as the final product is vulcanizingly molded. In this vulcanizingly molding process, the thickness of ring shaped rubber compound is reduced to one fifth (⅕) to two thirds (⅔) by compressing the ring shaped rubber compound in the axial direction under high temperature. And then, vulcanizingly molded one is magnetized S-poles and N-poles alternately in circumference.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an encoder made of rubbermaterial on which the S-poles and the N-poles are alternately magnetizedin circumference, and a method of manufacturing the said encoder. Moreparticularly, the present invention relates to an encoder as the beforedescribed, and, its magnetic force is strong when it is magnetized andvariation and/or irregularity of magnetism in the circumferentialdirection of it is slight. Also the present invention relates to amethod of manufacturing the said encoder.

[0003] 2. Description of the Related Art

[0004] Conventionally, an encoder made of rubber material and having amagnetism has been manufactured as follows: first, an appropriate amountof magnetic powders such as ferrites are mixed into rubber material, andunvulcanized rubber compound in a sheet shape is formed by roll sheetingprocess using the said mixture. Next, this unvulcanized rubber compoundin a sheet shape is cut into square rubber thread like a slit. Thissquare rubber band is formed into a rubber band ring by temporarilyjoining the opposite ends of it together. Then, this rubber band ring iscompression-molded and vulcanizingly molded from the upward and downwarddirections using a mold. And the S-poles and the N-poles are alternatelymagnetized in circumference onto this vulcanizingly molded rubber ring.

[0005] An encoder made of rubber material and having a magnetismmanufactured by the above-described conventional manufacturing methodhas problems such as those described as follows:

[0006] When the rubber band ring is formed by temporarily joining theopposite ends of square rubber band, which was cut like a slit fromsheet shaped rubber compound, the said rubber band ring is made fromunvulcanized rubber compound made by mixing magnetic powders and rubbermaterial with a little considering about the arrangement and alignmentof the magnetic powders. Therefore, the vulcanizingly molded rubberring, which was obtained by compression-molding and vulcanizinglymolding the said rubber band ring causes the malfunction that themagnetic force varies in the circumferential direction when the S-polesand the N-poles are alternately magnetized in a circumference. As aresult, it was difficult to obtain an encoder made of rubber materialand having a magnetism, which can produce uniform and powerful magneticforces anywhere in the circumferential direction when it is magnetized.

[0007] Avoiding such a default, another formative method has beenemployed. In this formative method, unvulcanized rubber compoundcontaining magnetic powders is formed into a thin sheet shape using aroller or an extruder for the purpose of enhancing the degree oforientation of magnetism, and a rubber band ring is formed by punchingthis sheet in a ring shape.

[0008] According to this method, it is possible that the arrangement ofmagnetic powders such as ferrites or the like is made to hold thedirectional orientation. Moreover, there are no joining portions, whichis made by joining the opposite ends of square rubber band and makingthe direction of arrangement of the magnetic powders to be irregular.Therefore, one has found satisfaction to some extent.

[0009] However, in this method, it is necessary to make the sheet shapedrubber compound comparatively thin in order to enhance the degree oforientation of the magnetic powders in the process in which the sheetshaped rubber compound is formed by rolling or extruding using a rolleror an extruder. Therefore, in any way, the extrusion of a sheet istroublesome. Moreover, also in the molding, many malfunctions such asthe case where a plurality of sheets being superimposed has to beinputted into the roller or the extruder and the like have beenoccurred.

[0010] Furthermore, during the extrusion of a thin sheet, it easilyengages a wrinkle, a bubble or the like. So that, when it iscompression-molded, there has been a problem that the orientation ofmagnetism is easily dislocated.

SUMMARY OF THE INVENTION

[0011] The present invention has been made in consideration of thebefore described circumstances. And an object of the present inventionis to provide an encoder made of rubber material and having a magnetismwhich can be manufactured in a simplified manufacturing step and, whenthe S-poles and the N-poles are alternately magnetized in circumference,whose magnetic force is strong and which exerts approximately uniformmagnetism at any position in the circumferential direction, and whosevariation of the magnetism is slight in the circumferential direction.Another object of the present invention is to provide a manufacturingmethod for manufacturing the before described encoder.

[0012] The present invention has solved the above-described problems byusing a ring shaped rubber compound comprised of unvulcanized rubberinto which magnetic powders are mixed and having a thickness of 1.5times to 5 times thicker than the thickness of an encoder, which isfinally produced from the said ring shaped rubber, and the said ringshaped rubber compound is hot-pressed, and vulcanizingly molded asfollows. The said ring shaped rubber compound is heat compressed byusing upper mold and lower mold, which pressing the said ring shapedrubber compound in the axial direction, thereby its thickness is reducedto one fifth (⅕) to two thirds (⅔), and it is flown uniformly in a largeamount in the radial direction of the said ring shaped rubber compoundunder a high temperature.

[0013] The manufacturing steps of the present invention will beseparated into each step, and described in detail with reference to thedrawings as follows.

[0014] The present invention provides an encoder made of rubber materialand having a magnetism for forming a pulse train and generating a signalby the magnetic force showing an example in FIG. 6, also the presentinvention provides its manufacturing method.

[0015] In a method that the present invention provides, first,unvulcanized rubber into which the magnetic powders are mixed is formedinto a sheet shaped rubber compound having a predetermined thicknessusing a roller or an extruder. Alternatively, the said sheet shapedrubber compound having a predetermined thickness can be formed byextruding the said unvulcanized rubber by extruder, and then rolling anextrusion-molded unvulcanized rubber by roller.

[0016] Now, the predetermined thickness as the before described meansthat the thickness t1 (as shown in FIG. 1) of the sheet shaped rubbercompound is 1.5 times to 5 times thicker than a thickness t (as shown inFIG. 4) of the encoder made of rubber material and having a magnetismwhich is the final product.

[0017] It should be noted that it is preferable that, in this step, asheet shaped rubber compound is formed while the directional orientationof the magnetic powders is arranged. According to the present invention,the final product of the encoder made of rubber material ismanufactured, succeeding to the before described step of forming a sheetshaped rubber compound having a predetermined thickness, by cutting outa ring shaped rubber compound from the said sheet shaped rubbercompound, hot-pressing and vulcanizingly molding the said ring shapedrubber compound, and magnetizing the S-poles and the N-poles alternatelyin circumference onto the said vulcanizingly molded ring, which areexplained in detail in the following.

[0018] In the before described step of forming a sheet shaped rubbercompound having a predetermined thickness, if the directionalorientation of the mixed magnetic powders in the unvulcanized rubber isarranged, such as regulated, a variation, such as irregularity, ofmagnetism in the circumferential direction of the final product ofencoder, which is manufactured by and through the succeeding steps asthe before described, becomes smaller. So that, in the before describedstep of forming a sheet shaped rubber compound, it is preferable to forma sheet shaped rubber compound with arranging and regulating thedirectional orientation of magnetic powders in the unvulcanized rubber.

[0019] Next, from a sheet shaped rubber compound having theafore-mentioned thickness ti, a ring shaped rubber compound 1 as shownin FIG. 1 is cut out.

[0020] Subsequently, as shown in FIG. 2, the ring shaped rubber compound1 is inputted into molds 2 a and 2 b, and as shown in FIG. 3, it isheated and compressed, and vulcanizingly molded in parallel by the molds2 a and 2 b along with the direction of the central axis O, that is, inthe directions shown by arrows X and Y.

[0021] The heating and compression at this step is performed in thetemperature range of 150° C. -230° C. and in the pressure range of1MPa.200Mpa. And the thickness of the ring shaped rubber compound 1 isreduced to one fifth (⅕) to two thirds (⅔) of the thickness t1 of thering shaped rubber compound 1, that is the thickness t1 is reduced tothe thickness t of the encoder made of rubber material 3 which is thefinal product.

[0022] Owing to this, the ring shaped rubber compound 1 is pressed undera high temperature, and flown uniformly in a large amount in the radialdirection of the ring shaped rubber compound 1 as shown by arrows Z andW in FIG. 1, and then formed.

[0023] Next, onto this vulcanizingly molded one, shown by the referencenumeral 3 in FIG. 3, although it is not shown, the S-poles and theN-poles are alternately magnetized in circumference, and the encoder 3as shown in FIG. 4 which is made of rubber material and having amagnetism, which is the final product, is obtained.

[0024] Thus, in a manufacturing method of the present invention, thering shaped rubber compound 1 having the predetermined thickness(thickness corresponding to 1.5 times to 5 times of the thickness t ofthe encoder 3 made of rubber material which is the final product) issubjected to be compressed under a high temperature and pressed into athickness of ⅕-⅔ of the thickness of ring shaped rubber compound. Inthis hot-pressing step, the ring shaped rubber compound is flownuniformly in a large amount in the radial direction shown by the arrowsZ and W in FIG. 1, and then formed. Owing to this, even if there isuneven blending of the magnetic powders in the circumferential directionin the state of the ring shaped rubber compound 1, it can be removed inthe step that the thickness of ring shaped rubber compound is reduced to⅕-⅔ by the before described compression step under a high temperature.Moreover, even if there are an engaged bubble and/or wrinkle in the ringshaped rubber compound, or any variation and/or irregularity of thethickness or the like in the ring shaped rubber compound, they are alsoremoved by this compression step under a high temperature.

[0025] Therefore, an encoder made of rubber material and having anexcellent performance which can exert powerful magnetic forces, andapproximately uniform magnetic forces at any position in thecircumferential direction, is manufactured by magnetizing the N-polesand the S-poles alternately in circumference onto the vulcanizinglymolded ring, which has been obtained by hot-pressing the ring shapedrubber compound and reducing its thickness to one fifth (⅕) to twothirds (⅔) as the before described.

[0026] An encoder made of rubber material and having a magnetismprovided by the present invention is manufactured by the manufacturingmethod described above.

[0027] As described above, it is preferable to set the thickness t1 ofthe ring shaped rubber compound, which is identical with the thicknessof the sheet shaped rubber compound (unvulcanized rubber) at the rangebetween 1.5 times to 5 times thicker than the thickness t of the encodermade of rubber material, which is the final product, and toheat-compress and vulcanizingly mold the said ring shaped rubbercompound reducing its thickness to one fifth (⅕) to two thirds (⅔), inorder to obtain and manufacture the encoder made of rubber material andhaving an excellent performance such as exerting powerful magneticforces, and approximately uniform magnetic forces at any position in thecircumferential direction when magnetizing the N-poles and S-polesalternately in circumference onto the vulcanizingly molded one.

[0028] It should be noted that if necessary, when the ring shaped rubbercompound 1 is molded with heating and compression, a reinforcing ring 4consisted of metals or the like as shown in FIG. 2, FIG. 8, FIG. 4, andFIG. 6 can be also inputted within the mold 2, and vulcanized andadhered at the same time.

[0029] As described above, according to the present invention, it canprovide an encoder made of rubber material and having a magnetism, whenthe S-poles and N-poles are alternately magnetized in thecircumferential direction, whose magnetic force is strong and whichexerts approximately uniform magnetic force at any position in thecircumferential direction and whose variation or irregularity of themagnetism is slight in the circumferential direction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a perspective view showing a ring shaped rubber compoundcut out from a sheet shaped rubber compound in a manufacturing method ofthe present invention;

[0031]FIG. 2 is a sectional view showing a state where a ring shapedrubber compound is inputted into a mold in a manufacturing method of thepresent invention;

[0032]FIG. 3 is a sectional view showing a state where a ring shapedrubber compound was heated and compressed;

[0033]FIG. 4 is a sectional view showing an example of an encoder madeof rubber material of the present invention;

[0034]FIG. 5 is a sectional view showing the other state where a ringshaped rubber compound is heated and compressed in a manufacturingmethod of the present invention; and

[0035]FIG. 6 is a perspective view showing the other preferred exampleof an encoder made of rubber material of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Hereinafter, the preferred examples of the present invention willbe described farther in detail.

[0037] In a manufacturing method of the present invention,unvulcanizined rubber into which magnetic powders are mixed can beprepared by blending the magnetic powders into a polymer such as NBR(acrylonitrile-butadiene rubber) or ACM (acrylic acid ester co-polymer)or H-NBR (hydrogenation acrylonitrile-butadiene rubber) or FKM (fluorinerubber), and mixing with a rubber agent.

[0038] Now, as a magnetic powder, for example, ferrite can be employed.

[0039] It is desirable that a blending ratio of the magnetic powders isset to 70%-98% by weight. If the mixing ratio of the magnetic powders isless than 70% by weight, it is not preferable because the magnetic forceof the final product (encoder made of rubber material and having amagnetism) is insufficient, and to the contrary, if it is more than 98%by weight, it is not preferable because the unvlcanized rubber is toohardened, and the processing ability becomes poor.

[0040] Upon forming unvulcanized rubber, into which the magnetic powderssuch as ferrite or the like is mixed, to a sheet shaped rubber compound,it is preferable as described above that the arrangement of the magneticpowders is to be orientated, that is, that the magnetic powders are tobe arranged and orientated in a formed sheet shaped rubber compound. Sothat, it is preferable to form a sheet shaped rubber compound having thebefore described thickness t1 using anyone of the following steps.

[0041] In the case where a sheet shaped rubber compound is formed usinga roller, it is preferable that a rubber raw material in a state ofbeing unvulcanized into which the magnetic powders are mixed is in turnpassed through a plurality of rollers, gradually made into a sheet andformed into a sheet shaped rubber compound having a thickness t1(FIG. 1) of 1.5 -5 times of the thickness t (FIG. 4) of the encoder madeof rubber material which is the final product.

[0042] In this case, it is preferable to process it so that the sheetshaped rubber compound has the afore-mentioned thickness t1 bypassingmore than two times through a plurality of rollers, rather than formingthe sheet shaped rubber compound having the afore-mentioned thickness t1only by one passing through roller.

[0043] In the case where an extruder is employed, it is preferable toform a sheet shaped rubber compound having the before describedthickness t1 by extrusion-molding using an extruder having a simplifiedshape outlet such as a plane shaped outlet.

[0044] Alternatively, in the case where an extruder is employed as thebefore described, after it is extrusion-molded by an extruder having asimplified shape such as a plane shaped outlet or a round shaped outletinto a plate shaped or thread shaped, it can be formed into a sheetshaped rubber compound having the afore-mentioned thickness t1 byrolling the said plate shaped or thread shaped extruded rubber compoundat least one passing through roller.

[0045] The ring shaped rubber compound 1 as shown in FIG. 1 is formedfrom the sheet shaped rubber compound, which has been formed as thebefore described, by and through the following steps, for example. Thering shaped rubber compound 1 is trimmed from the sheet shaped rubbercompound by using trimming die and putting the said trimming die to thesheet shapes rubber compound from a plane direction.

[0046] Alternatively, the ring shaped rubber compound 1 as shown in FIG.1 can be formed by cutting it out from the sheet shaped- rubbercompound, which has been formed as the before described, in the desiredsize.

[0047] The ring shaped rubber compound 1 formed as described above isinputted within the molds 2 a and 2 b. If necessary, the ring shapedrubber compound 1 formed as described above is inputted within the molds2 a and 2 b with the reinforcing ring 4 as shown in FIG. 2.

[0048] Then, as shown by the arrows X and Y in FIG. 3, it is heatcompressed in the axial direction along with the direction of the centeraxis O, so that its thickness is reduced to be one fifth (⅕) to twothirds (⅔), and it is flown and vulcanizingly molded.

[0049] At that time, if the ring shaped rubber compound 1 was inputtedwithin the molds 2 a and 2 b with the reinforcing ring 4, the said ringshaped rubber compound 1 and reinforcing ring 4 are adhered at the sametime. At this time, the heat compression is performed in the temperaturerange of 150° C. -230° C. and in the pressure range of 1MPa-200MPa.

[0050] Subsequently, the encoder made of rubber material 3 (FIG. 4) isobtained by magnetizing the S-poles and the N-poles alternately incircumference onto this vulcanizingly molded one.

[0051] This encoder made of rubber material 3 is strong at the magneticforce, and exerts approximately uniform magnetic force at any positionin the circumferential direction, and its variation of the magnetism isslight at any position in the circumferential direction.

[0052] It should be noted that in the manufacturing method of an encodermade of rubber material and having a magnetism according to the presentinvention described above, an encoder made of rubber material is formedon the flange portion of the reinforcing ring 4, as shown in FIG. 6, byemploying the molds 2 a and 2 b as shown in FIG. 2 and FIG. 3.

[0053]FIG. 5 shows a manufacturing method of an encoder made of rubbermaterial and having a magnetism according to the present invention inwhich the reinforcing ring 41 having a cylindrical part is employed andthe encoder made of rubber material of the present invention is providedand arranged cylindrically onto the outer surface of the saidcylindrical part of reinforcing ring 41 in the axial direction.

[0054] In this case, an upper mold and a lower mold in a shape as shownin FIG. 5 are employee In this case, even if a mold cavity of the mold21 is in a deep channel shape, since similar to the afore-mentionedexample, the ring shaped rubber compound 1 is heated and compressedunder a high temperature and pressed, and flown and vulcanizinglymolded, the magnetic powders within the ring shaped rubber compound 1 isflown in a certain arrangement with the directional orientation into themold cavity and filled within the mold cavity.

[0055] Although the present invention has been described in connectionwith the particular preferred embodiments by referring to theaccompanying drawings, it should be understood that the presentinvention is not limited to those embodiments, but various changes andmodifications may be made without departing from the true spirit andscope of the invention as defined in the appended claims.

[0056] For example, in the embodiment described so far, the unvulcanizedrubber is prepared to include ferrites as the magnetic powders This isbecause ferrites are available at low cost, are capable of retaining themagnetism when they are magnetized, and can be treated easily when therolling or extruding process takes place. Any other types of magneticmaterials that meet the above requirements may also be used.

[0057] And, in the afore-mentioned examples, when the ring shaped rubbercompound 1 is hot-pressed, and vulcanizingly molded, the reinforcingring 4 consisted of metals or the like is also inputted within the mold2 and vulcanizingly adhered at the same time. In this case, thereinforcing ring 4 is used for the purpose of providing the mechanicalstrength for the finished encoder made of rubber material and having amagnetism according to the present invention. Hence, after only the ringshaped rubber compound 1 is inputted into the mold 2 and hot-pressed,and further vulcanizingly molded, this valcanizingly molded-one may beadhered by adhering it on the flange section of the reinforcing ring 4.

What is claimed is:
 1. An encoder made of rubber material and having amagnetism, characterized that said encoder is obtained by forming asheet shaped rubber compound having a predetermined thickness usingunvulcanized rubber into which magnetic powders are mixed and rolling orextruding said unvulcanized rubber by roller or extruder, cutting out aring shaped rubber compound from the said sheet shaped compound withmaintaining the said thickness, hot-pressing, and vulcanizingly moldingthe said ring shaped rubber compound thereby reducing its thickness toone fifth to two thirds by using a mold, and magnetizing the S-poles andthe N-poles alternately in circumference onto the said vulcanizinglymolded ring.
 2. An encoder made of rubber material and having amagnetism, characterized that said encoder is obtained by forming asheet rubber compound having a predetermined thickness usingunvulcanized rubber into which magnetic powders are mixed and extrudingsaid unvulcanized rubber by extruder and then rolling anextrusion-molding unvulcanized rubber by roller, cutting out a ringshaped rubber compound from the said sheet shaped compound withmaintaining the said thickness, hot-pressing, and vulcanizingly moldingthe said ring shaped rubber compound thereby reducing its thickness toone fifth to two thirds by using a mold, and magnetizing the S-poles andthe N-poles alternately in circumference onto the said vulcanizinglymolded ring.
 3. A method of manufacturing an encoder made of rubbermaterial and having a magnetism, which comprises: forming a sheet shapedrubber compound having a predetermined thickness using unvulcanizedrubber into which magnetic powders are mixed and rolling or extrudingsaid unvulcanized rubber by roller or extruder; cutting out a ringshaped rubber compound from the said sheet shaped compound withmaintaining the said thickness; hot-pressing, and vulcanizingly moldingthe said ring shaped rubber compound thereby reducing its thickness toone fifth to two thirds by using a mold; and magnetizing the S-poles andthe N-poles alternately in circumference onto the said vulcanizinglymolded ring.
 4. A method of manufacturing an encoder made of rubbermaterial and having a magnetism, which comprises: forming a sheet shapedrubber compound having a predetermined thickness using unvulcanizedrubber into which magnetic powders are mixed and extruding saidunvulcanized rubber by extruder and then rolling an extrusion-moldedunvulcanized rubber by roller; cutting out a ring shaped rubber compoundfrom the said sheet shaped compound with maintaining the said thickness;hot-pressing, and vulcanizingly molding the said ring shaped rubbercompound thereby reducing its thickness to one fifth to two thirds byusing a mold; and magneting the S-poles and the N-poles alternately incircumference onto the said vulcanizingly molded ring.